排序演算法 – 快速排序(C++)

// 單向掃描就地重排int Partitation_1Way(int array[], int nIdxLeft, int nIdxRight){assert(NULL != array);if (nIdxLeft == nIdxRight)return nIdxLeft;// Take the last element as middle value.int nMiddleVal = array[nIdxRight];int nIdxSmall = nIdxLeft - 1;// Always true in loop://     elements within [nIdxLeft, nIdxSmall] are smaller than nMidVal.//     elements within [nIdxSmall+1, nIdxBig] are bigger than nMidVal.for (int nIdxBig = nIdxLeft; nIdxBig<=nIdxRight; nIdxBig++){if (array[nIdxBig]<=nMiddleVal){nIdxSmall ++;if (nIdxSmall != nIdxBig){int nTemp = array[nIdxSmall];array[nIdxSmall] = array[nIdxBig];array[nIdxBig] = nTemp;}}}return nIdxSmall;}// 雙向掃描就地重排int Partitation_2Way(int array[], int nIdxLeft, int nIdxRight){assert(NULL != array);if (nIdxLeft == nIdxRight)return nIdxLeft;// Take the first element as middle value.int nMidVal = array[nIdxLeft];int nIdxBackward = nIdxLeft;int nIdxForward = nIdxRight;for ( ; nIdxBackward < nIdxForward; ){// forward find the small one from tail, move frontwhile (nIdxBackward < nIdxForward && array[nIdxForward] > nMidVal)nIdxForward--;array[nIdxBackward] = array[nIdxForward];// backward find the big one from head, move back.while (nIdxBackward < nIdxForward && array[nIdxBackward] < nMidVal)nIdxBackward++;array[nIdxForward] = array[nIdxBackward];}array[nIdxBackward] = nMidVal;return nIdxBackward;}void QuickSort(int array[], int nIdxLeft, int nIdxRight){if (NULL == array || nIdxLeft == nIdxRight)return;if (nIdxLeft < nIdxRight){int nIdxMid = Partitation_1Way(array, nIdxLeft, nIdxRight);//int nIdxMid = Partitation_2Way(array, nIdxLeft, nIdxRight);QuickSort(array, nIdxLeft, nIdxMid-1);QuickSort(array, nIdxMid+1, nIdxRight);}}